Fabrication by irradiation is faster and more energy efficient than traditional methods, and owing to the efficiency of radiation modulation, the process lends itself to high degree of automation. With direct control of irradiation by data about object cross-sections automatically generated from object configuration in computer-aided design (CAD) systems, and with simultaneous fabrication of whole layers, objects can be formed hundreds of times faster than with traditional manufacturing processes and totally automatic. Expediency is crucial in many areas including modeling and prototyping and is the key to competitiveness in automotive and other industries. Many configurations like those with enclosed cavities or incorporating several different materials cannot be made monolithically with other methods.
Several methods and apparatus have been developed for the production of three-dimensional objects by irradiation of photopolymers that cross-link and solidify upon irradiation. Some of them are based on solidification in a tank point by point by optical scanning with two intersecting beams; or by mechanical scanning with irradiation means within the liquid when solidification can be accomplished by whole layers or in other large portions (U.S. Pat. No. 4,801,477). In other systems objects are formed layer by layer solidifying the top layer of photopolymer in a tank, either by simultaneous irradiation of whole layers with irradiation means in contact with the liquid in order to minimize shrinkage distortion, and adding liquid on top for subsequent layers (U.S. Pat. No. 4,752,498), or by solidifying each layer point by point with fast scanning of the top surface open to air, and dropping down the solidified layer so that radiation is always applied to the same plane (U.S. Pat. No. 4,575,330).
Those systems usually employ a prefabricated container filled with photopolymer liquid, and a substrate upon which object is formed is positioned within the liquid in the container. The fabrication process is intermittent, with deposition and irradiation alternating, and substrate (or container together with irradiation means) is usually repositioned after each layer is formed so that the container extends up to the irradiated surface, limiting access to formed portions. Containers and substrates exceed biggest objects formed and large quantities of photopolymer and moving mass are involved.
To provide high accuracy of fabrication, objects are formed in very thin layers requiring a great number of photopolymer depositions. With requirements of multiple fast movements, very small layer thickness, and simultaneous irradiation of the whole layer (for fast fabrication) in maximal proximity (for higher accuracy), containers extending up to the irradiated surface and large moving mass make the deposition process difficult to implement and time consuming. Consequently, fabrication is complicated and slow, and much faster continuous fabrication requiring continuous deposition becomes impractical.
Elimination of the container would provide a significant simplification of the apparatus, contribute to drastic reduction of fabrication time, and open the way to continuous fabrication free of burdening multiple successive depositions.